Enhanced variable power zoom lens

ABSTRACT

The present invention is directed to provide an enhanced variable power zoom lens that is lightweight as a whole, and especially, has its focusing lens optics reduced in weight so as to relieve of a load on a focusing drive system, and that has its anti-vibration lens optics reduced in both diameter and weight so as to relieve of a load on an anti-vibration drive system and downsize the same. The enhanced variable power zoom lens is adapted to have the foremost or first lens group of positive refractivity, the second lens group of negative refractivity, the third lens group of positive refractivity, the fourth lens group of negative refractivity, and the fifth lens group arranged in this sequence from a position closer to the object where a distance between each pair of the adjacent lens groups is varied during zooming from the wide-angle end to the telephoto end, each lens group comes closer to the object at the telephoto end than at the wide-angle end, the third lens group and the fourth lens group separating the farthest apart from each other at the intermediate zooming range, and the fourth lens group is moved closer to the image plane for shifting from infinity focusing to proximity focusing.

FIELD OF THE INVENTION

The present invention relates to a compact and enhanced variable powerzoom lens having a zoom ratio of 10× or even greater and an angle ofview of 75 degrees or even wider at the wide-angle end, which issuitable for use in 35 mm cameras, video cameras, electronic stillcameras, and the like.

BACKGROUND ART

As one example of prior art focusing systems for a zoom lens, an upfrontlens focusing system is well-known in the art where the foremost groupof lens pieces positioned the closest to the object to photograph isdisplaced for focusing. When designed in an application of anauto-focusing zoom lens, the upfront lens focusing zoom lens must haveits large and heavy foremost lens group moved along the optical axis,and this makes it difficult to achieve instantaneous focusing.

In order to overcome the aforementioned disadvantage, inner and rearfocusing systems that force the second foremost lens group and/or thefurther succeeding one(s) are to be displaced instead have come to beknown. Employing the inner or rear focusing system brings about asuccessful result in achieving an instantaneous auto focusing zoom lensof which focusing lens groups can be generally down-sized and reduced inweight so as to reduce the load on an actuating motor for an autofocusing mechanism.

On the other hand, there generally arises a problem with such anenhanced variable power zoom lens that user's hands are liable to shakeduring photographing at the telephoto end. In order to avoid the adverseeffect on the resultant image due to a shake of photographer's hands, avariety of methods have been devised for displacing part of the lensoptics in an approximately perpendicular direction to the optical axisso that rays imaged on light receptor are shifted on the same, therebycanceling an image blur due to a shake of hands of the photographer.

It is also strongly desired that the enhanced variable power zoom lensis compact so as not to spoil user's convenience.

Especially, some digital single lens reflex cameras having thestate-of-the-art live view feature carry out contrast auto-focusing,namely, bring rays into focus by wobbling. Hence, the greater weight ofthe focusing lens group(s) should requires the larger actuator todisplace the focusing lens group(s), which results in the focusingsystems becoming bulky as a whole; and therefore, it is stronglydesirable that the focusing lens group(s) is reduced in weight.

Further developed has been a compact, high performance, and enhancedvariable power zoom lens which has lens groups respectively of positive,negative, positive, and positive refractive powers arranged in order forzooming; and this prior art enhanced variable power zoom lens, whenattached to a lens-exchangeable digital single lens reflex camera withan APS-C size image sensor built in, attains angle of view as wide as 76degrees that is equivalent to 28 mm in a single lens reflex cameradedicated for 35 mm film, and zoom ratio as high as 7×, and has backfocal equivalent to that of a lens-exchangeable single lens reflexcamera (e.g., see Patent Document 1 listed below).

Some other prior art enhanced variable power zoom lens developed so farincludes a photographing lens that has anti-vibration function andimproved performance and that has lens groups respectively of positive,negative, negative, positive, negative, and positive refractive powersfor zooming or otherwise positive, negative, negative, positive,positive refractive powers for the same purpose where the third foremostlens group is used for focusing while the fifth lens group is dedicatedto anti-vibration operation; and its variable magnification power issuper-enhanced to such an extent of being as high as approximately 12×without compromising a capability of inner-focusing to photograph aproximal object (e.g., see Patent Document 2).

Still another prior art enhanced variable power zoom lens is the onethat is as high as 10× in zoom ratio and that has lens groupsrespectively of positive, negative, positive, negative, and positiverefractive powers for zooming; that is, the lens groups consists of atleast the 1st lens group G1 of positive refractivity, the 2nd lens groupG2 of negative refractivity, the 3rd lens group G3 of positiverefractivity, the 4th lens group G4 of negative refractivity, and the5th lens group G5 of positive refractivity arranged in order from aposition closer to the object where as the photographing mode is shiftedfrom the wide-angle to the telephoto to vary the magnification power,the 1st lens group G1 and the 2nd lens group G2 spread farther apartfrom each other, the 2nd lens group G2 and the 3rd lens group G3 comecloser to each other, the 3rd lens group G3 and the 4th lens group G3also spread farther apart from each other, and the 4th lens group G4 andthe 5th lens group G5 come closer to each other (e.g., see PatentDocument 3).

Further another prior art enhanced variable power zoom lens is the onethat consists of four lens groups, namely, the 1st lens group to the 4thlens group respectively having positive, negative, positive, andpositive refractive powers in sequence from a position closer to theobject; and the 1st and 2nd lens groups separate farther away from eachother so as to vary the magnification power from the wide-angle to thetelephoto while concurrently the 3rd lens group axially moves tocompensate for variation in the image plane in association with varyingthe magnification power, and the 2nd lens group moves orthogonal to theoptical axis and simultaneously makes a minute turn about a single pointon the optical axis within or near the 2nd lens group to compensate fora blur of the image; i.e., provided is a method in which the primarypower-varying lens group in the positive lead type zoom lens, namely,the 2nd lens group of negative refractivity serves as an anti-vibrationlens and moves orthogonal to the optical axis (e.g., see Patent Document4).

Yet another prior art enhanced variable power zoom lens is the one withthe 2nd lens group comprising lens subsets one of which, namely, anon-focusing lens subset 2 a serves as an anti-vibration lens; and thiszoom lens is compact since displacement of its focusing lens group isnot extremely increased during focusing (e.g., see Patent Document 5).The enhanced variable power zoom lens has the 1st lens group of positiverefractivity, the 2nd lens group of negative refractivity, and one ormore succeeding lens groups of positive refractivity as a whole arrangedin sequence from a position closer to one conjugate point as the originof a longer half of a conjugate distance upon varying the magnificationpower from the wide-angle to the telephoto, the 1st and 2nd lens groupsseparate farther apart from each other while the 2nd lens group and thesucceeding lens group(s) come closer to each other; and the 2nd lensgroup comprises lens subsets, namely, the lens subset 2 a of negativerefractivity and another lens subset 2 b of negative refractivity closerto the other conjugate point as the terminal point of a shorter half ofthe conjugate distance than the lens subset 2 a so that the lens subset2 b is dedicated to focusing under specific relative conditions amongthe focal length at the wide-angle end, the focal length at thetelephoto end, and the focal length of the lens subset 2 a.

Furthermore, there is another prior art enhanced variable power zoomlens of the reduced variation in image magnification ratio for focusing,which has the 1st lens group of positive refractive power, the 2nd lensgroup of negative refractive power, and the succeeding two or more lensgroups arranged in sequence from a position closer to the object whereall the lens groups axially move during zooming so as to vary a distancebetween any pair of the adjacent lens groups while the second rearmostlens group closer to the image plane axially move for focusing (e.g.,see Embodiment 7 in Patent Document 6 listed below). The enhancedvariable power zoom lens disclosed in Patent Document 6 has thedownsized focusing and anti-vibration lens groups although it stillattains an enhanced zoom ratio as high as 10×.

LIST OF CITED DOCUMENTS OF THE RELATED ART

Patent Document 1—Preliminary Publication of Unexamined PatentApplication No. 2005-331697;

Patent Document 2—Preliminary Publication of Unexamined PatentApplication No. 2003-329933;

Patent Document 3—Preliminary Publication of Unexamined PatentApplication No. H10-0133109;

Patent Document 4—Preliminary Publication of Unexamined PatentApplication No. H05-0232410;

Patent Document 5—Preliminary Publication of Unexamined PatentApplication No. 2000-028923; and

Patent Document 6—Preliminary Publication of Unexamined PatentApplication No. 2009-265652.

In the enhanced variable power zoom lens disclosed in Patent Document 1,since the 2nd lens group serves as a focusing lens and consists of fivelens pieces, the focusing lens is heavy and increases in variation ofthe image magnification ratio, and this is undesirable for thecontrast-detect automatic focusing.

In the enhanced variable power zoom lens disclosed in Patent Document 2,the 3rd lens group consisting of two lens pieces serves as a focusinglens and realizes weight reduction of a kind, but the focusing lens ofapproximately 10 grams is still heavy and insufficient in weightreduction demanded for the focusing lens. In order to further reduceweight, the 5th lens group is dedicated to anti-vibration, and thisattempt still fails to attain sufficient weight reduction. The zoom lensconfigured in this manner is also hard to have the increased opticalperformance including an ability to compensate for optical aberrations.

In the enhanced variable power zoom lens disclosed in Patent Document 3,the 3rd lens group consisting of three lens pieces serves as a focusinglens, and the focusing lens is 10 grams or even heavier, which isunsatisfactory in an application directed to contract-detect automaticfocusing. It is also unacceptable as a compact and enhanced variablepower zoom lens.

In the enhanced variable power zoom lens disclosed in Patent Document 4,the 2nd lens group of negative refractive power is suitable for servingas an anti-vibration lens because of the reduced development of comaticaberration upon moving eccentrically. However, the 2nd lens group in theenhanced variable power zoom lens essentially consists of four or morelens pieces, and thus, the zoom lens is disadvantageous in that it ishard to downsize the anti-vibration mechanism.

In the enhanced variable power zoom lens disclosed in Patent Document 5,the lens subset 2 a must have the increased lens diameter to obtain asufficient quantity of light around the image plane at the wide-angleend, and thus, the zoom lens is disadvantageous in that it is hard todownsize the anti-vibration mechanism.

In the enhanced variable power zoom lens (Embodiment 7) disclosed inPatent Document 6, the 3rd lens group of negative refractivityconsisting of two lens pieces serves as an anti-vibration lens, and theanti-vibration lens is reduced in weight. However, since the lens groupcloser to the object than the aperture stop is used to correct a blur ofthe image due to a shake of photographer's hands and thus of the camera,it encounters a difficulty in inhibiting varied astigmatism duringstabilizing the image against the camera shake, and thus, the opticalperformance of the zoom lens during image stabilizing operation isunsatisfactory. In addition, since the zoom lens has a filter of a largediameter and has six lens groups respectively of positive, negative,negative, positive, negative, and negative refractive powers forzooming, the zoom lens is disadvantageous in that it is hard to providea compact lens barrel.

The present invention is made to overcome the aforementioneddisadvantages in the prior art enhanced variable power zoom lens, andaccordingly, it is an object of the present invention to provide theimproved enhanced variable power zoom lens that is lightweight as awhole, and especially, has its focusing lens optics reduced in weight soas to relieve of a load on a focusing drive system, and that has itsanti-vibration lens optics reduced in both diameter and weight so as torelieve of a load on an anti-vibration drive system and downsize thesame.

It is another object of the present invention to provide the improvedenhanced variable power zoom lens that is upgraded in optical capabilityof compensating for aberrations and in performance as represented by thereduced variation in image magnification ratio during focusing as wellas facile handling and manipulation.

SUMMARY OF THE INVENTION

The present invention provides an enhanced variable power zoom lens thatis adapted to have the first lens group G1 of positive refractivity, thesecond lens group G2 of negative refractivity, the third lens group G3of positive refractivity, the fourth lens group G4 of negativerefractivity, and the fifth lens group G5 arranged in sequence from aposition closer to the object where a distance between each pair of theadjacent lens groups is varied during zooming from the wide-angle to thetelephoto where each lens group comes closer to the object at thetelephoto than at the wide-angle, the third lens group G3 and the fourthlens group G4 separate the farthest apart from each other at theintermediate zooming range, and the fourth lens group G4 is moved closerto the image plane for focusing on from the infinity to an proximalobject.

The enhanced variable power zoom lens according to the present inventionis configured as mentioned above so as to reduce weight in whole and inpart, especially, having its focusing lens optics lightened to relieveof a load on a focusing drive system and having its anti-vibration lensoptics reduced in both diameter and weight to relieve of a load on ananti-vibration drive system, thereby attaining the downsizing of theanti-vibration drive system.

In accordance with the present invention, the enhanced variable powerzoom lens is upgraded in optical capability of correcting aberrationsand in performance to attain the reduced variation in imagemagnification ratio during focusing as well as facile handling andmanipulation, and is capable of producing a clear image with the reducedeffects of the optical aberrations.

Some aspects of the present invention will be outlined. First, severalcommon articles of the present invention in these aspects will bediscussed.

The enhanced variable power zoom lens generally has the foremost orfirst lens group G1 of positive refractivity, the second lens group G2of negative refractivity, the third lens group G3 of positiverefractivity, the fourth lens group G4 of negative refractivity, and thefifth lens group G5 arranged in sequence from a position closer to theobject.

During zooming from the wide-angle to the telephoto, each pair of theadjacent lens groups come apart from or closer to each other, and eachlens group move closer to the object at the telephoto than at thewide-angle. Designed to take such optical posture and behavior forzooming, the zoom lens at the wide-angle end can be compact although itstill provides an angle of view of 75 degrees or wider and a zoom ratioof 10× or even higher.

The third lens group G3 and the fourth lens group G4 separate thefarthest away from each other at the intermediate zooming range.Designed to take such optical posture for zooming, the zoom lens is ableto compensate for distortion of the imaging plane at the intermediatezooming range.

Also, for focusing on from the infinity to the proximal object, thefourth lens group G4 moves toward the image plane. With a design wherethe fourth lens group G4 of negative refractivity, which is positionedright behind the third lens group G3 of positive refractivity and closerto the image filed, serves as a focusing lens, it is facilitated toreduce an outer lens diameter of the focusing lens.

The third lens group G3 includes separate subsets of lens pieces,namely, the foremost lens subset G3A of positive refractivity, thesecond foremost lens subset G3B of positive refractivity, and thesucceeding lens subset G3C arranged in sequence from a position closerto the object. The lens subset G3B of lens pieces 3B is moved orthogonalto the optical axis to correct an imaging position against a shake ofphotographer's hands. With a design where the lens subset G3B, which ispositioned right behind the lens subset G3A of lens pieces 3A ofpositive refractivity and closer to the image plane, serves as ananti-vibration lens, it becomes possible to avoid the necessity ofhaving the anti-vibration lens of the increased diameter.

The lens subset G3B of lens pieces 3B includes a composite lens ofpositive and negative lens pieces arranged in sequence from a positioncloser to the object. Configured in this manner, the zoom lens becomeslightweight and is capable of compensating for variation in chromaticaberration well upon correcting an image blur due to a shake ofphotographer's hands. A front surface of the foremost one of the lenspieces 3B, the closest to the object in the lens subset G3B, isaspherical. Configured in this manner, the zoom lens is capable ofcompensating for variation in spherical and comatic aberrations wellupon correcting an image blur due to a shake of photographer's hands.

During zooming, the third lens group G3 and the fifth lens group G5 movealong the same cam structure. A design to make the third and fifth lensgroups G3 and G5 displace by the same distance enables these lens groupsto be integrated in a single unit. The lens groups integrated in thesingle unit in this manner also permits the cam structure to besimplified, which brings about reduction in the maximum diameter of thelens barrel. In addition, the third and fifth lens groups G3 and G5experience minimized eccentricity to each other, and this results indegradation of the optical performance due to fabrication tolerancebeing avoided as much as possible.

The present invention in several aspects will be stated below:

(1) The fifth lens group G5 has positive refractive power. In one aspectof the invention, an entrance pupil positioned increasingly closer tothe object leads to a greater telecentric effect, and this effectivelyprevents incident beams from falling upon light receptors/beam receivingelements in imbalanced positions.

(2) In another aspect of the present invention, the zoom lens meetrequirements as expressed in the following formulae:0.7<f3/fw<2.0  (1)0.07<|f4|/ft<0.3  (2)where f3 is a focal length of the third lens group, f4 is the focallength of the fourth lens group, fw is the focal length of the entireoptics at the wide-angle end, and ft is the focal length of the entireoptics at the telephoto end.

In this aspect of the present invention, when f3/fw exceeds the lowerlimit defined in the formula (1), the zoom lens has its focusing lensadvantageously downsized, but instead, encounters difficulty incompensating for various types of aberration such as comatic aberration.When f3/fw exceeds the upper limit, the zoom lens can advantageouslycompensate for aberration, but instead becomes hard to downsize thefocusing lens.

When |f4|/ft exceeds the lower limit, an actuator is advantageouslydownsized, but instead, it is hard to compensate for the aberration.When |f4|/ft exceeds the upper limit, the zoom lens can advantageouslycompensate for aberration, but instead has a displacement of the lensoptics increased for focusing, which leads to an increase in dimensionsof the actuator. Allowing for all the above, in this aspect of theinvention, a clear image with the reduced aberration can be effectivelyproduced.

(3) In another aspect of the present invention, the third lens group G3has a composite lens in a position the closest to the image plane, acomposition interface of the composite lens being a divergent surface;and the zoom lens meets a requirement as expressed in the followingformula:n1−n2>0.25  (3)where n1 is a refractive index of a negative lens piece of the compositelens at d-line, and n2 is a refractive index of a positive lens piece ofthe composite lens at d-line.

In this aspect of the invention, when (n1−n2) becomes lower to such anextent of exceeding the lower limit as defined in the formula (3), thethird lens group G3 is, upon proximity focusing, likely to loseperformability to adjust imaging with more striking positive sphericalaberration to such an extent of encountering difficulty in compensatingfor the spherical aberration. Thus, when it meets the requirement, thezoom lens can effectively produce a clear image with the reducedaberration.

(4) In still another aspect of the present invention, the fourth lensgroup G4 has a composite lens consisting of a positive lens piece and anegative lens piece, having at least one of surfaces shaped aspherical.

In this aspect, the fourth lens group G4 with the lens piece having atleast one of its major surfaces made aspherical is capable of inhibitingwell from varying in spherical aberration and comatic aberrationthroughout the entire range of an object distance. Thus, configured inthis manner, the zoom lens can effectively produce a clear image withthe reduced aberration.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing a first embodiment of a zoomlens according to the present invention.

FIG. 2 a illustrates graphs of various types of aberration when the zoomlens of the first embodiment at the wide-angle end for zooming is ininfinity focus.

FIG. 2 b illustrates graphs of the various types of aberration when thezoom lens of the first embodiment at the wide-angle end for zooming isin proximity focus.

FIG. 3 a illustrates graphs of the various types of aberration when thezoom lens of the first embodiment at the intermediate range for zoomingis in infinity focus.

FIG. 3 b illustrates graphs of the various types of aberration when thezoom lens of the first embodiment at the intermediate range for zoomingis in proximity focus.

FIG. 4 a illustrates graphs of the various types of aberration when thezoom lens of the first embodiment at the telephoto end for zooming is ininfinity focus.

FIG. 4 b illustrates graphs of the various types of aberration when thezoom lens of the first embodiment at the telephoto end for zooming is inproximity focus.

FIG. 5 is a cross-sectional view showing a second embodiment of the zoomlens according to the present invention.

FIG. 6 a illustrates graphs of various types of aberration when the zoomlens of the second embodiment at the wide-angle end for zooming is ininfinity focus.

FIG. 6 b illustrates graphs of the various types of aberration when thezoom lens of the second embodiment at the wide-angle end for zooming isin proximity focus.

FIG. 7 a illustrates graphs of the various types of aberration when thezoom lens of the second embodiment at the intermediate range for zoomingis in infinity focus.

FIG. 7 b illustrates graphs of the various types of aberration when thezoom lens of the second embodiment at the intermediate range for zoomingis in proximity focus.

FIG. 8 a illustrates graphs of the various types of aberration when thezoom lens of the second embodiment at the telephoto end for zooming isin infinity focus.

FIG. 8 b illustrates graphs of the various types of aberration when thezoom lens of the second embodiment at the telephoto end for zooming isin proximity focus.

FIG. 9 is a cross-sectional view showing a third embodiment of the zoomlens according to the present invention.

FIG. 10 a illustrates graphs of various types of aberration when thezoom lens of the third embodiment at the wide-angle end for zooming isin infinity focus.

FIG. 10 b illustrates graphs of the various types of aberration when thezoom lens of the third embodiment at the wide-angle end for zooming isin proximity focus.

FIG. 11 a illustrates graphs of the various types of aberration when thezoom lens of the third embodiment at the intermediate range for zoomingis in infinity focus.

FIG. 11 b illustrates graphs of the various types of aberration when thezoom lens of the third embodiment at the intermediate range for zoomingis in proximity focus.

FIG. 12 a illustrates graphs of the various types of aberration when thezoom lens of the third embodiment at the telephoto end for zooming is ininfinity focus.

FIG. 12 b illustrates graphs of the various types of aberration when thezoom lens of the third embodiment at the telephoto end for zooming is inproximity focus.

FIG. 13 is a cross-sectional view showing a fourth embodiment of thezoom lens according to the present invention.

FIG. 14 a illustrates graphs of various types of aberration when thezoom lens of the fourth embodiment at the wide-angle end for zooming isin infinity focus.

FIG. 14 b illustrates graphs of the various types of aberration when thezoom lens of the fourth embodiment at the wide-angle end for zooming isin proximity focus.

FIG. 15 a illustrates graphs of the various types of aberration when thezoom lens of the fourth embodiment at the intermediate range for zoomingis in infinity focus.

FIG. 15 b illustrates graphs of the various types of aberration when thezoom lens of the fourth embodiment at the intermediate range for zoomingis in proximity focus.

FIG. 16 a illustrates graphs of the various types of aberration when thezoom lens of the fourth embodiment at the telephoto end for zooming isin infinity focus.

FIG. 16 b illustrates graphs of the various types of aberration when thezoom lens of the fourth embodiment at the telephoto end for zooming isin proximity focus.

BEST MODE OF THE INVENTION

The present invention will now be described in conjunction withembodiments, referring to the accompanying drawings.

In discussing each embodiment, the term ‘aspherical surface or aspheric’means a surface or state as expressed by the following formula:

$\begin{matrix}{x = {\frac{H^{2}/r}{1 + \sqrt{1 - {\left( {1 + k} \right)\left( {H/r} \right)^{2}}}} + {A_{4}H^{4}} + {A_{6}H^{6}} + {A_{8}H^{8}} + {A_{10}H^{10}}}} & (4)\end{matrix}$where x is the optical axis, H is a height from the optical axis in adirection orthogonal to the optical axis, r is a paraxial radius ofcurvature, k is a coefficient of the cone, and An is a factor of theaspherical surface raised to the n-th power.

Embodiment 1

A first embodiment of an enhanced variable power zoom lens consists ofthe foremost or first lens group G1 of positive refractivity, the secondlens group G2 of negative refractivity, the third lens group G3 ofpositive refractivity, the fourth lens group G4 of negativerefractivity, and the fifth lens group G5 of positive refractivityarranged in sequence from a position closer to the object.

The first lens group G1 consists of a composite lens of a negativemeniscus lens piece L1 having its convex surface directed toward theobject and a double-convex lens piece L2, and a positive meniscus lensL3 having its convex surface directed toward the object.

The second lens group G2 consists of a negative meniscus lens L4 havingits convex surface directed toward the object, a double-concave lens L5,a double-convex lens L6, and a negative meniscus lens L7 having itsconvex surface directed toward the image plane. The negative meniscuslens L4 positioned the closest to the object of all the lens pieces inthe second lens group G2 is a composite aspherical lens having its glasssurface closer to the object superposed with resin layer and shaped inaspherical surface.

An aperture stop is positioned right ahead of the foremost lens piece inthe third lens group G3. A design with the aperture stop positionedcloser to the object than the third lens group G3 facilitates reductionin diameter of the upfront lens of the zoom lens.

The third lens group G3 consists of a double-convex lens L8, a negativemeniscus lens L9 having its convex surface directed toward the object, acomposite lens consisting of a double-convex lens piece L10 and anegative meniscus lens piece L11 having its convex surface directedtoward the image plane, and a composite lens consisting of a negativemeniscus lens piece L12 having its convex surface directed toward theobject and a double-convex lens piece L13 arranged in sequence from aposition closer to the object. The double-convex lens L8, positioned theclosest to the object, of all the lens pieces in the third lens group G3is a glass molded aspherical lens that has both the front and rear majorsurfaces made aspherical in shape. The double-convex lens piece L10 is aglass molded aspherical lens that has its front major surface madeaspheric in shape. Correcting an image blur due to a shake ofphotographer's hands is conducted by moving the composite lens of thedouble-convex lens piece L10 and the negative meniscus lens piece L11 ina direction orthogonal to the optical axis.

The fourth lens group G4 consists of a positive meniscus lens L14 havingits convex surface directed toward the image plane and a double-concavelens L15 arranged in sequence from a position closer to the object. Thedouble-concave lens L15, positioned the closest to the image plane, ofall the lens pieces in the fourth lens group G4 is a compositeaspherical lens that has its rear surface made aspherical in shape.

The fifth lens group G5 consists of a double-convex lens L16 closer tothe object and a negative meniscus lens L17 having its convex surfacedirected toward the image plane.

The zoom lens of the first embodiment is implemented under conditions asexpressed by the numerical data as follows:f=18.4671 to 193.7966F No.=3.58 to 6.472ω=78.47 to 8.20

The zoom lens of the first embodiment is represented by the factors,namely, radius of curvature r, thickness (distance between lenssurfaces) d, refractive indices, nd and vd, as given as follows (anysurface number with a suffix of an asterisk (*) is for an asphericalsurface):

Surface Number r d nd vd Object Plane ∞ (d0)  1 140.6286 1.5000 1.9036631.31  2 72.7778 7.2029 1.49700 81.61  3 −395.7178 0.2000  4 61.53065.5571 1.61800 63.39  5 221.7716 (d5)   6* 90.6266 0.2000 1.51460 49.96 7 60.6266 1.2000 1.90366 31.31  8 13.8208 7.5749  9 −21.7485 0.90001.83481 42.72 10 240.9339 0.2000 11 52.2290 3.5618 1.92286 20.88 12−28.3941 1.5245 13 −17.8390 0.8000 1.83481 42.72 14 −33.0000 (d14) 15 ∞1.0000 (Aperture Stop)  16* 18.4782 4.0353 1.61881 63.85  17* −48.56510.7167 18 41.8835 0.9000 1.77250 49.62 19 22.8773 2.9125  20* 33.28733.3000 1.59201 67.02 21 −25.5242 0.8000 1.84666 23.78 22 −41.3225 0.526023 265.5713 0.8000 1.90366 31.31 24 14.7745 4.4219 1.51742 52.15 25−21.3443 (d25) 26 −1799.6857 2.2000 1.72825 28.32 27 −20.2692 0.70001.69680 55.46 28 16.8599 0.2500 1.51460 49.96  29* 18.1394 (d29) 3024.6924 4.7278 1.48749 70.44 31 −34.7332 0.5818 32 −25.1727 1.00001.83481 42.72 33 −195.8334 (BF)

The zoom lens of the first embodiment has the aspheric surfaces each ofwhich is characterized by a coefficient as given below:

Surface Number k A4 A6 A8 A10 6 0.0000 2.00246E−05 −4.07575E−081.35108E−10 2.54007E−13 16 −1.6765 1.73663E−05 −1.78587E−09 1.55565E−095.28154E−12 17 0.0000 4.00586E−05 −8.57830E−08 2.49011E−09 −1.89872E−1320 0.0000 −1.59299E−05 4.84995E−08 −1.30605E−09 9.03492E−12 29 0.0000−2.10416E−05 1.08897E−07 −6.52540E−09 5.29800E−11

The zoom lens of the first embodiment, when in infinity focus, has thelens surfaces of the lens pieces variably distanced as follows:

Wide-angle End Intermediate Range Telephoto End f 18.4671 69.9995193.7966 d0 ∞ ∞ ∞ d5 1.0000 34.0712 64.3105 d14 25.4255 6.3450 1.7000d25 1.4000 4.7187 1.4999 d29 9.5946 6.2759 9.4947 BF 18.3076 40.056253.5093

The zoom lens of the first embodiment, when in proximity focus (i.e.,upon proximity photographing as close as 0.5 meters to the object), hasthe lens surfaces of the lens pieces variably distanced as follows:

Wide-angle End Intermediate Range Telephoto End f 18.1576 60.2317105.9540 d0 384.9800 349.2410 310.1970 d5 1.0000 34.0712 64.3105 d1425.4255 6.3450 1.7000 d25 1.6487 6.5210 9.1651 d29 9.3459 4.4736 1.8296BF 18.3076 40.0562 53.5093

The zoom lens of the first embodiment is designed to take values foreach of the formulae (1) to (3) that have been given above:f3/fw=1.063  (1)|f4|/ft=0.136  (2)n1−n2=0.386  (3)

Embodiment 2

A second embodiment of the enhanced variable power zoom lens accordingto the present invention consists of the foremost or first lens group G1of positive refractivity, the second lens group G2 of negativerefractivity, the third lens group G3 of positive refractivity, thefourth lens group G4 of negative refractivity, and the fifth lens groupG5 of negative refractivity arranged in sequence from a position closerto the object.

The first lens group G1 consists of a composite lens of a negativemeniscus lens piece L1 having its convex surface directed toward theobject and a double-convex lens piece L2, and a positive meniscus lensL3 having its convex surface directed toward the object.

The second lens group G2 consists of a negative meniscus lens L4 havingits convex surface directed toward the object, a double-concave lens L5,a double-convex lens L6, and a negative meniscus lens L7 having itsconvex surface directed toward the image plane arranged in sequence froma position closer to the object. The negative meniscus lens L4,positioned the closest to the object, of all the lens pieces in thesecond lens group G2 is a composite aspherical lens having its surfacecloser to the object made aspherical in shape.

The third lens group G3 consists of a positive meniscus lens L8 havingits convex surface directed toward the object, a composite lensconsisting of a double-convex lens piece L9 and a negative meniscus lenspiece L10 having its convex surface directed toward the image plane, anda composite lens consisting of a negative meniscus lens piece L11 havingits convex surface directed toward the object and a double-convex lenspiece L12 arranged in sequence from a position closer to the object.

The positive meniscus lens L8, positioned the closest to the object, ofall the lens pieces in the third lens group G3 is a glass moldedaspherical lens that has both the front and rear major surfaces madeaspherical in shape. The double-convex lens piece L9 is a glass moldedaspherical lens that has its front major surface made aspheric in shape.Correcting an image blur due to a shake of photographer's hands isconducted by moving the composite lens of the double-convex lens pieceL9 and the negative meniscus lens piece L10 in a direction orthogonal tothe optical axis.

The aperture stop is right behind the positive meniscus lens L8positioned the closest to the object, of all the lens pieces in thethird lens group G3.

The fourth lens group G4 consists of a double-convex lens L13 closer tothe object and a double-concave lens L14 positioned behind it. Thedouble-concave lens L14, positioned the closest to the image plane, ofall the lens pieces in the fourth lens group G4 is a glass moldedaspherical lens that has its rear surface made aspherical in shape.

The fifth lens group G5 consists of a double-convex lens L15, acomposite lens consisting of a double-concave lens piece L16 and adouble-convex lens piece L17, and a double-convex lens L18 arranged insequence from a position closer to the object.

The zoom lens of the second embodiment is implemented as expressed bythe numerical data as follows:f=18.4727 to 193.6981F No.=3.52 to 6.492ω=78.56 to 8.16

The zoom lens of the second embodiment is represented by the factors,namely, radius of curvature r, thickness (distance between lenssurfaces) d, refractive indices, nd and vd, as given as follows (anysurface number with a suffix of an asterisk (*) is for an asphericalsurface):

Surface Number r d nd vd Object Plane ∞ (d0)  1 130.1822 1.5000 1.9036631.31  2 70.3192 8.0000 1.49700 81.61  3 −618.3880 0.2000  4 67.18746.0000 1.61800 63.39  5 355.9279 (d5)  6* 78.4467 0.2000 1.51460 49.96 7 51.8370 1.2000 1.90366 31.31  8 14.0622 7.7373  9 −21.1050 0.90001.83400 37.34 10 75.2303 0.3731 11 45.7447 3.6000 1.92286 20.88 12−26.8250 1.4978 13 −17.7689 0.8000 1.83481 42.72 14 −32.1245 (d14) 15*23.2369 2.5000 1.61881 63.85 16* 500.0000 2.0000 17 (Aperture Stop) ∞3.0000 18* 52.1695 3.0000 1.61881 63.85 19 −23.8364 1.0000 1.80809 22.7620 −38.5827 2.0746 21 44.7975 0.8000 1.90366 31.31 22 13.6368 4.50001.56883 56.04 23 −33.1024 (d23) 24 69.4378 2.2000 1.80809 22.76 25−28.7775 0.8000 1.82080 42.71 26* 18.2404 (d26) 27 124.7143 2.40001.49700 81.61 28 −29.7638 1.1000 29 −22.8912 1.0000 1.83481 42.72 3019.4397 3.8000 1.51680 64.20 31 −121.9600 0.2000 32 28.8664 3.70001.60562 43.71 33 −500.0000 (BF)

The zoom lens of the second embodiment has the aspheric surfaces each ofwhich is characterized by a coefficient as given below:

Surface Number k A4 A6 A8 A10 6 0.0000 1.28933E−05 −1.52071E−08−3.90660E−11 6.69323E−13 15 −0.8659 2.48260E−05 2.75427E−07 −3.35843E−095.70805E−11 16 0.0000 4.56781E−05 2.93462E−07 −3.64965E−09 6.44333E−1118 0.0000 −1.30798E−05 3.93669E−09 6.54017E−11 −7.11351E−13 26 0.0000−7.16565E−06 −3.20200E−08 −1.39534E−09 1.50295E−11

The zoom lens of the second embodiment, when in infinity focus, has thelens surfaces of the lens pieces variably distanced as follows:

Wide-angle End Intermediate Range Telephoto End f 18.4727 69.9995193.6981 d0 ∞ ∞ ∞ d5 0.9000 36.5480 65.6130 d14 24.7181 7.3691 4.0245d23 3.0460 5.1714 1.0000 d26 6.7531 4.6278 8.7992 BF 13.6198 36.053049.4455

The zoom lens of the second embodiment, when in proximity focus (i.e.,upon proximity photographing as close as 0.5 meters to the object), hasthe lens surfaces of the lens pieces variably distanced as follows:

Wide-angle End Intermediate Range Telephoto End f 18.1240 59.9839110.4075 d0 384.8810 344.1490 305.0380 d5 0.9000 36.5480 65.6130 d1424.7181 7.3691 4.0245 d23 3.3285 6.9987 7.6876 d26 6.4706 2.8005 2.1116BF 13.6198 36.0530 49.4455

The zoom lens of the second embodiment is designed to take values foreach of the formulae (1) to (3) that have been given above:f3/fw=1.053  (1)|f4|/ft=0.157  (2)n1−n2=0.335  (3)

Embodiment 3

A third embodiment of the enhanced variable power zoom lens according tothe present invention consists of the foremost or first lens group G1 ofpositive refractivity, the second lens group G2 of negativerefractivity, the third lens group G3 of positive refractivity, thefourth lens group G4 of negative refractivity, and the fifth lens groupG5 of positive refractivity arranged in sequence from a position closerto the object.

The first lens group G1 consists of a composite lens of a negativemeniscus lens piece L1 having its convex surface directed toward theobject and a double-convex lens piece L2, and a positive meniscus lensL3 having its convex surface directed toward the object.

The second lens group G2 consists of a negative meniscus lens L4 havingits convex surface directed toward the object, a negative meniscus lensL5 having its convex surface directed toward the image plane, adouble-convex lens L6, and a negative meniscus lens L7 having its convexsurface directed toward the image plane arranged in sequence from aposition closer to the object. The negative meniscus lens L5 in thesecond lens group G2 is a glass molded aspherical lens having its frontsurface closer to the object and its rear surface closer to the imagefiled made aspherical in shape.

The third lens group G3 consists of a double-convex lens L8, a negativemeniscus lens L9 having its convex surface directed toward the object, acomposite lens consisting of a double-convex lens piece L10 and anegative meniscus lens piece L11 having its convex surface directedtoward the image plane, and a composite lens consisting of a negativemeniscus lens piece L12 having its convex surface directed toward theobject and a double-convex lens piece L13 arranged in sequence from aposition closer to the object. The positive meniscus lens L8, positionedthe closest to the object, of all the lens pieces in the third lensgroup G3 is a glass molded aspherical lens that has both the front andrear major surfaces made aspherical in shape. Correcting an image blurdue to a shake of photographer's hands is conducted by moving thecomposite lens of the double-convex lens piece L10 and the negativemeniscus lens piece L11 in a direction orthogonal to the optical axis.

The aperture stop is right behind the negative meniscus lens L9 andcloser to the image plane.

The fourth lens group G4 has a composite lens consisting of adouble-convex lens piece L14 closer to the object and a double-concavelens piece L15 positioned behind it. The double-concave lens L15,positioned the closest to the image plane, of all the lens pieces in thefourth lens group G4 is a glass molded aspherical lens that has its rearsurface made aspherical in shape.

The fifth lens group G5 consists of a double-convex lens L16, acomposite lens consisting of a double-concave lens piece L17 and adouble-convex lens piece L18, and a double-convex lens L19 arranged insequence from a position closer to the object.

The zoom lens of the third embodiment is implemented as expressed by thenumerical data as follows:f=18.4635 to 193.6592F No.=3.62 to 6.522ω=78.51 to 8.25

The zoom lens of the third embodiment is represented by the factors,namely, radius of curvature r, thickness (distance between lenssurfaces) d, refractive indices, nd and vd, as given as follows (anysurface number with a suffix of an asterisk (*) is for an asphericalsurface):

Surface Number r d nd vd Object Plane ∞ (d0)  1 122.8583 1.5000 1.9036631.31  2 63.6327 8.0000 1.49700 81.61  3 −479.7631 0.2000  4 60.07026.0000 1.61800 63.39  5 326.6006 (d5)  6 83.7787 1.0000 1.80420 46.50  712.3144 7.4805  8* −22.1241 1.0000 1.73077 40.50  9* −64.4650 0.2000 10215.4697 3.1478 1.92286 20.88 11 −30.2010 1.5773 12 −17.6709 0.80001.83481 42.72 13 −33.1232 (d13) 14* 17.2167 4.0000 1.61881 63.85 15*−125.5742 0.2000 16 48.4757 1.0000 1.77250 49.62 17 19.0841 3.3000 18(Aperture Stop) ∞ 1.5000 19* 45.5870 2.8000 1.61881 63.85 20 −27.02851.0000 1.80518 25.46 21 −49.9440 1.7247 22 32.4233 0.8000 1.90366 31.3123 15.2360 3.6847 1.51680 64.20 24 −27.5987 (d24) 25 81.6411 2.20001.80809 22.76 26 −24.5463 0.8000 1.82080 42.71 27* 17.6072 (d27) 2857.2163 2.1666 1.48749 70.44 29 −86.5299 1.0000 30 −27.0636 1.10001.80610 33.27 31 29.0154 4.0000 1.51742 52.15 32 −58.1335 0.2000 3334.7156 3.1887 1.62004 36.30 34 −500.0000 (BF)

The zoom lens of the third embodiment has the aspheric surfaces each ofwhich is characterized by a coefficient as given below:

Surface Number k A4 A6 A8 A10 8 0.0000 7.25755E−05 −1.27843E−067.32783E−09 −2.81756E−11 9 0.0000 3.49690E−05 −1.24580E−06 6.63675E−09−2.34217E−11 14 −1.5994 2.13130E−05 4.89855E−08 −2.49609E−10−2.54671E−12 15 0.0000 2.60502E−05 −1.46189E−08 3.24684E−10 −8.07360E−1219 0.0000 −9.20242E−06 8.57474E−09 −1.54371E−10 1.03899E−12 27 0.0000−9.97587E−06 −4.27259E−08 −8.86898E−10 1.03922E−11

The zoom lens of the third embodiment, when in infinity focus, has thelens surfaces of the lens pieces variably distanced as follows:

Wide-angle End Intermediate Range Telephoto End f 18.4635 69.9769193.6592 d0 ∞ ∞ ∞ d5 0.9000 35.4429 58.6609 d13 26.2891 7.2099 2.5000d24 4.5393 6.1188 1.0612 d27 6.2013 4.6218 9.6795 BF 4.5543 35.049654.5230

The zoom lens of the third embodiment, when in proximity focus (i.e.,upon proximity photographing as close as 0.5 meters to the object), hasthe lens surfaces of the lens pieces variably distanced as follows:

Wide-angle End Intermediate Range Telephoto f 18.1515 60.5992 113.6489d0 381.9470 345.9890 308.0110 d5 0.9000 35.4429 58.6609 d13 26.28917.2099 2.5000 d24 4.8281 8.1797 8.4976 d27 5.9125 2.5609 2.2431 BF14.5543 35.0496 54.5230

The zoom lens of the third embodiment is designed to take values foreach of the formulae (1) to (3) that have been given above:f3/fw=1.112  (1)|f4|/f t=0.142  (2)n1−n2=0.387  (3)

Embodiment 4

A fourth embodiment of the enhanced variable power zoom lens accordingto the present invention consists of the foremost or first lens group G1of positive refractivity, the second lens group G2 of negativerefractivity, the third lens group G3 of positive refractivity, thefourth lens group G4 of negative refractivity, and the fifth lens groupG5 of positive refractivity arranged in sequence from a position closerto the object.

The first lens group G1 consists of a composite lens of a negativemeniscus lens piece L1 having its convex surface directed toward theobject and a double-convex lens piece L2, and a positive meniscus lensL3 having its convex surface directed toward the object.

The second lens group G2 consists of a negative meniscus lens L4 havingits convex surface directed toward the object, a double-concave lens L5,a double-convex lens L6, and a negative meniscus lens L7 having itsconvex surface directed toward the image plane arranged in sequence froma position closer to the object. The negative meniscus lens L4positioned the closest to the object, of all the lens pieces in thesecond lens group G2 is a composite aspherical lens having its frontsurface closer to the object made aspherical in shape.

An aperture stop is right ahead of the third lens group G3 and closer tothe object than the same. A design with the aperture stop in a positioncloser to the object than the third lens group G3 facilitates reductionin a diameter of the upfront lens of the zoom lens.

The third lens group G3 consists of a double-convex lens L8, a negativemeniscus lens L9 having its convex surface directed toward the object, acomposite lens consisting of a double-convex lens piece L10 and anegative meniscus lens piece L11 having its convex surface directedtoward the image plane, and a composite lens consisting of a negativemeniscus lens piece L12 having its convex surface directed toward theobject and a double-convex lens piece L13 arranged in sequence from aposition closer to the object. The double-convex lens L8, positioned theclosest to the object, of all the lens pieces in the third lens group G3is a glass molded aspherical lens that has both its front major surfacecloser to the object and its rear major surface closer to the imageplane made aspherical in shape. The double-convex lens L10 is a glassmolded aspherical lens that has its front surface made aspherical inshape. Correcting an image blur due to a shake of photographer's handsis conducted by moving the composite lens of the double-convex lenspiece L10 and the negative meniscus lens piece L11 in a directionorthogonal to the optical axis.

The fourth lens group G4 consists of a positive meniscus lens L14 closerto the object and having its convex surface directed toward the imageplane and a double-concave lens piece L15 positioned behind it. Thedouble-concave lens L15, positioned the closest to the image plane, ofall the lens pieces in the fourth lens group G4 is a compositeaspherical lens that has its rear surface made aspherical in shape.

The fifth lens group G5 consists of a double-convex lens L16 and anegative meniscus lens L17 having its convex surface directed toward theimage plane.

The zoom lens of the fourth embodiment is implemented as expressed bythe numerical data as follows:f=18.4656 to 193.7618F No.=3.58 to 6.472ω=78.45 to 8.20

The zoom lens of the fourth embodiment is represented by the factors,namely, radius of curvature r, thickness (distance between lenssurfaces) d, refractive indices, nd and vd, as given as follows (anysurface number with a suffix of an asterisk (*) is for an asphericalsurface):

Surface Number r d nd vd Object Plane ∞ (d0)  1 141.2619 1.5000 1.9036631.31  2 71.0032 7.3049 1.49700 81.61  3 −403.3371 0.2000  4 60.98525.6822 1.61800 63.39  5 232.8153 (d5)  6* 78.7650 0.2000 1.51460 49.96 7 55.0310 1.2000 1.88300 40.80  8 13.4213 7.6368  9 −21.7620 0.90001.83400 37.34 10 448.6204 0.2000 11 52.5441 3.2720 1.92286 20.88 12−29.2978 1.0276 13 −18.4015 0.8000 1.88300 40.80 14 −36.5889 (d14) 15(Aperture Stop) ∞ 1.0000 16* 20.6887 4.8000 1.61881 63.85 17* −40.33670.9389 18 −42.9919 1.0000 1.74400 44.79 19 −120.0000 1.6300 20* 36.90423.3000 1.59201 67.02 21 −26.0822 0.8000 1.84666 23.78 22 −37.7319 0.334023 108.8218 0.8000 1.90366 31.31 24 13.3365 5.1053 1.51742 52.15 25−22.9306 (d25) 26 −8357.4904 2.2000 1.72825 28.32 27 −18.3036 0.70001.69680 55.46 28 15.6342 0.2500 1.51460 49.96 29* 16.7161 (d29) 3023.7440 4.7241 1.48749 70.44 31 −37.2401 0.6221 32 −25.8488 1.00001.88300 40.80 33 −185.0333 (BF)

The zoom lens of the fourth embodiment has the aspheric surfaces each ofwhich is characterized by a coefficient as given below:

Surface Number k A4 A6 A8 A10 6 0.0000 2.08367E−05 −4.57755E−081.75054E−10 1.98364E−13 16 −1.6344 1.80716E−05 2.70181E−08 1.74662E−09−3.38851E−12 17 0.0000 4.18327E−05 −5.69981E−08 2.75644E−09 −9.39699E−1220 0.0000 −1.94427E−05 5.94040E−08 −1.82677E−09 1.34942E−11 29 0.0000−2.42872E−05 3.00275E−07 −1.46151E−08 1.38187E−10

The zoom lens of the fourth embodiment, when in infinity focus, has thelens surfaces of the lens pieces variably distanced as follows:

Wide-angle End Intermediate Range Telephoto End f 18.4656 69.9889193.7618 d0 ∞ ∞ ∞ d5 1.0000 34.1618 64.2114 d14 24.0788 6.1436 1.7000d25 1.4000 4.5190 1.8070 d29 9.7948 6.6758 9.3878 BF 17.9032 39.217951.8628

The zoom lens of the fourth embodiment, when in proximity focus (i.e.,upon proximity photographing as close as 0.5 meters to the object), hasthe lens surfaces of the lens pieces variably distanced as follows:

Wide-angle End Intermediate Range Telephoto End f 18.1467 60.0008104.7262 d0 386.6960 350.1550 311.9050 d5 1.0000 34.1618 64.2114 d1424.0788 6.1436 1.7000 d25 1.6235 6.1137 8.6097 d29 9.5713 5.0811 2.5851BF 17.9032 39.2179 51.8628

The zoom lens of the fourth embodiment is designed to take values foreach of the formulae (1) to (3) that have been given above:f3/fw=1.010  (1)|f4|/ft=0.126  (2)n1−n2=0.386  (3)

The invention claimed is:
 1. An enhanced variable power zoom lens adapted to have the foremost or first lens group of positive refractivity, the second lens group of negative refractivity, the third lens group of positive refractivity, the fourth lens group of negative refractivity, and the fifth lens group arranged in this sequence from a position closer to the object, a distance between each pair of the adjacent lens groups being varied during zooming from the wide-angle end to the telephoto end, each lens group coming closer to the object at the telephoto end than at the wide-angle end, the third lens group and the fourth lens group separating the farthest apart from each other at the intermediate zooming range, and the fourth lens group being moved closer to the image plane for shifting from infinity focusing to proximity focusing.
 2. The enhanced variable power zoom lens according to claim 1, wherein the fifth lens group exhibits negative refractivity.
 3. The enhanced variable power zoom lens according to claim 1, wherein the zoom lens meets requirements as expressed in the following formulae: 0.7<f3/fw<2.0 0.07<|f4|/ft<0.3 where f3 is a focal length of the third lens group, f4 is the focal length of the fourth lens group, fw is the focal length of the entire optics at the wide-angle end, and ft is the focal length of the entire optics at the telephoto end.
 4. The enhanced variable power zoom lens according to claim 1, wherein the third lens group has a composite lens in a position the closest to the image plane, a composition interface of the composite lens being a divergent surface; and the zoom lens meets a requirement as expressed in the following formula: n1−n2>0.25 where n1 is a refractive index of a negative lens piece of the composite lens at d-line, and n2 is a refractive index of a positive lens piece of the composite lens at d-line.
 5. The enhanced variable power zoom lens according to claim 1, wherein the fourth lens group has a composite lens of positive and negative lens pieces, and at least one of surfaces of the composite lens is made aspherical in shape. 